The invention relates to a mechanical tappet, especially for actuating the lifting of a pump piston of a fuel pump in an internal combustion engine. The tappet has a sleeve-shaped tappet housing, which is constructed as a shaped sheet-metal part and which is supported in a tappet guide with an essentially cylindrical outer casing surface, and a driving roller supported so that it can rotate, as well as a stroke-transmission component, which is produced separately from the tappet housing and which is inserted into the tappet housing and which has a driven-side contact surface for the pump piston.
A tappet of this type is know from DE 103 45 089 A1. The tappet provided there is used as an actuating element of a known high-pressure fuel pump for the transverse force-free transmission of a cam stroke to the pump piston and features a sleeve-shaped tappet housing constructed as a shaped sheet-metal part. This housing has, in comparison with most extruded tappet housings of such roller tappets, both a high potential for lightweight construction and also a significant potential for cost savings. Someone skilled in the art can point out these advantageous properties immediately through a comparison of the tappet provided in the cited publication with a tappet as is known from DE 197 29 793 A1 with an extruded and consequently relatively thick-walled tappet housing.
The tappet in the publication noted first above nevertheless features a few serious disadvantages in connection with the driving roller. These include, essentially, that the driving roller is supported non-centered in the stroke-transmission component inserted in the tappet housing and slides accordingly with its peripheral surface in a corresponding recess of the stroke-transmission component. As is known, such a support of the driving roller, however, is extraordinarily difficult to align, because a certain rotation of the driving roller can be guaranteed only when the contact friction between the cam and the driving roller is always greater than the contact friction between the driving roller and the stroke-transmission component under all operating conditions of the internal combustion engine or the fuel pump. If corresponding alignment of the contact partners is not possible, then the stoppage of the driving roller at least at some times and counteracting the actual goal of reducing the friction must be taken into account with the correspondingly high risk of contact wear relative to the cam and/or the stroke-transmission component. In addition, for such a non-centered support of the driving roller in the stroke-transmission component, corresponding precautions must be taken for captive mounting of the driving roller on the tappet.